JP3013596B2 - Transmission ultrasonic flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type ultrasonic wave which emits ultrasonic waves into a fluid from an outer wall of a pipe, receives the ultrasonic waves on the outer wall of the pipe, and whose propagation time is proportional to the flow velocity or flow rate of the fluid. The present invention relates to an acoustic flow meter, and more particularly to an improvement thereof.

[0002]

2. Description of the Related Art FIGS. 9 and 10 are schematic diagrams showing a conventional example of a transmission type ultrasonic flowmeter (also simply referred to as an ultrasonic flowmeter). FIG. 9 shows an ultrasonic coupling / reception device 2a, 2b for receiving ultrasonic waves emitted into a fluid and propagating through the fluid.
This is an example in which fluids are arranged opposite to each other at a fixed distance on the same line at the top of the outer wall of the pipe 1 for guiding the fluid through the pipe 0. Further, the one shown in FIG. 10 is configured such that the transducers 2a and 2b which receive ultrasonic waves emitted in the fluid and reflected on the inner wall of the pipe are connected to the top of the outer wall of the pipe 1 for guiding the fluid through the acoustic coupling material 10. This is an example in which they are arranged opposite to each other on a different line at a fixed distance.

[0003] The transducers 2a, 2a,
As shown in FIG. 11, for example, as shown in FIG. 11, a block (hereinafter simply referred to as a wedge) 4 of an epoxy resin or the like generally used as an ultrasonic transmission material is provided with PZT (P
b (Zr · Ti) formed by bonding a ultrasonic transducer 3, which is a piezoelectric element, such as 0 _3). FIG. 11A is a side sectional view, and FIG. 11B is a top view. In such a configuration, the ultrasonic waves emitted from the transducer 2a are transmitted to the transducer 2b.
, And the time difference between the time at which the ultrasonic wave emitted from the transducer 2b reaches the transducer 2a is proportional to the flow rate or flow rate of the fluid 20 flowing through the pipe 1. The measurement principle of the ultrasonic flow meter is to measure the flow velocity or the flow rate from the time difference.

[0004]

However, in such an ultrasonic flowmeter as described above, the ultrasonic wave (direct wave reception) that propagates through the fluid from one transducer and is received by the other transducer is used. On the other hand, ultrasonic waves (so-called wraparound waves) that propagate along the inner and outer walls of the pipe or with multiple reflections at the thick part of the pipe are usually superimposed as noise. The influence of this loop wave will be described below with reference to FIGS. As shown in FIGS. 12 and 13, the ultrasonic wave emitted from the ultrasonic transducer 3 propagates directly as the received wave W, and the rest is received as the loop waves W1, W2, and W3 by the other transducer (not shown). Is done. Figure 1 shows the components of the loop wave
As shown in FIGS. 3 (a) and 3 (b), a wave W1 propagating with multiple reflections at the thick portion of the tube, a wave W2 propagating along the outer wall surface 16 and a wave W3 propagating along the inner wall surface 15 of the tube And mixed waves. Of these wraparound waves, as a wave superimposed on the direct reception, the tail of the wave received in the time zone before the direct reception (the tail of the wave extends to the time domain of the direct reception) And waves propagating in the circumferentially thick portion of the pipe. It has been found that the latter decreases when the directivity of transmission is increased.

FIG. 14 shows the relationship between the direct wave reception Sr in the ultrasonic flowmeter as shown in FIGS. 9 and 10 and the roundabout wave Rr of the pipe received in the time zone before the direct wave reception. As shown in the figure, the trailing of the looping wave Rr of the pipe directly overlaps with the received wave Sr, so that the S / N of the received wave is reduced. FIG. 15 shows an ultrasonic wave (hereinafter also referred to as a sound ray) emitted from an ultrasonic transducer in a conventional transducer.
FIGS. 3A and 3B are explanatory views for explaining a propagation mode of the ultrasonic transducer. FIG. 3A is a side sectional view of the ultrasonic transducer, and FIG. In the figure, θt is the angle of incidence of the ultrasonic wave of the ultrasonic transducer 3 with respect to the vertical line of the pipe longitudinal axis, and u and t are sound rays emitted from the ultrasonic transducer 3 at a certain directional angle with respect to the pipe longitudinal axis direction. And d indicate the outer diameter of the ultrasonic transducer 3 respectively.

That is, each sound ray u1, u as indicated by an arrow
Reference numerals 2, u3, t1, t2, and t3 are near-field sound fields. A primary reflected wave having a large energy is incident on the ultrasonic vibrator 3, and becomes sound rays u3 and t3 traveling toward the transducer 2b on the receiving side. . By the way, since the sound rays u3 and t3 have a small incident angle to the pipe and are multiple-reflected with the ultrasonic vibrator, the tailing of the transmission wave tends to be long. As described above, since a part of the sound ray incident on the area indicated by A2 is directed to the transmitter / receiver 2b on the receiving side, each area indicated by A1, A2, and A3 eventually becomes the transmitter / receiver on the receiving side. This is the area of the sound ray heading to 2b, and it can be said that the sound ray easily forms a trail of the transmission wave. As described above, in the conventional one, the S / N ratio of the received wave is reduced due to the wraparound wave, particularly the tailing thereof, and the measurement accuracy of the propagation time of the direct received wave in proportion to the flow velocity or flow rate of the fluid is reduced. Measurement cannot be performed. SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve the directivity of transmission, reduce multiple reflections of ultrasonic waves in a transmitter / receiver, and reduce tailing of wraparound waves to improve measurement accuracy.

[0007]

According to a first aspect of the present invention, there is provided a pair of transmission / reception units which include an ultrasonic vibrator and a wedge to which the ultrasonic vibrator is adhered and which can transmit and receive ultrasonic waves. The wave devices are arranged opposite to each other on the outer wall surface of the pipe with their positions shifted from each other, and the propagation time of the sound wave from the ultrasonic transducer on the upstream side to the ultrasonic transducer on the downstream side and the upstream side from the ultrasonic transducer on the downstream side. In a transmission type ultrasonic flowmeter that measures the flow velocity or flow rate of a fluid from the difference with the propagation time of a sound wave to an ultrasonic transducer on the side, a wedge in at least one of the pair of transducers is disposed in a longitudinal direction of a pipe. It is characterized in that the cross-sectional shape is a fractional circle or a divided ellipse. Also,
A second invention is characterized in that at least one of the pair of transducers is tapered at the tip of a wedge.

[0008]

[Function] By devising the shape of the wedge so that the reflected wave of the emitted ultrasonic wave does not enter the ultrasonic vibrator,
The multiple reflection of the ultrasonic wave in the transmitter / receiver is reduced, and the trailing of the sneak wave is reduced to improve the measurement accuracy.

[0009]

1 is a block diagram showing an embodiment of the present invention. FIG. 1A is a side sectional view and FIG. 1B is a top view. In the figure, 1 is a pipe, 2a and 2b are transducers, 3 is an ultrasonic transducer, 4 is a wedge, 5 is a case, 6 is a cable, 7
Denotes a sound absorbing material, 10 denotes an acoustic coupling material, and 20 denotes a fluid. That is, this embodiment corresponds to FIG.
As shown by a reference numeral 4A, the wedge 4 is formed by bending a tip portion thereof and filling a gap (also referred to as a sound absorbing material) 7 such as rubber between the bent portion 4A and the case 5. You. Thus, the curved portion 4A is formed by the sound absorbing material 7.
A part of the energy of the sound ray incident on the wedge 4 is absorbed, and the reflected wave at the curved portion 4A of the wedge 4 does not enter the ultrasonic vibrator 3 but repeats multiple reflections within the wedge 4 to repeat the reflection on the receiving side. It becomes a transmission propagation wave in the direction opposite to the propagation direction to the transducer 2b. As a result, not only the apparent propagation directivity is improved, but also the multiple reflection of the ultrasonic transducer in the transmitter / receiver is reduced, so that the trailing of the loop wave in the pipe 1 is reduced,
The S / N of the received wave will be improved.

The reason why the tip of the wedge 4 is bent will be described with reference to FIG. 2A is a side sectional view of the wedge, and FIG. 2B is a top view thereof. In the same figure, θt is the angle of incidence of the ultrasonic wave of the ultrasonic oscillator 3 with respect to the vertical line of the longitudinal axis of the pipe, and u and t are the directional angles from the ultrasonic transducer 3 at a certain directional angle with respect to the longitudinal axis of the pipe. The emitted sound ray, d indicates the outer diameter of the ultrasonic transducer 3, and R indicates the radius of a circle or the focal length of an ellipse. Wedge 4
Is a part of a circle or an ellipse (also called a divided circle or a divided ellipse), and the center of the circle or the focal point of the ellipse is located on an extension of the mounting surface 4B of the wedge 4 of the ultrasonic transducer 3, and the wedge is formed. A line T perpendicular to the mounting surface 4B and passing through the outer diameter position of the ultrasonic transducer 3 is a divided circle or divided ellipse in a range up to a point P where the line intersects a circular arc or an elliptical arc.

In this way, the sound rays u1, u2, t
Since 1,1 and t2 are reflected with the center line in the radial direction of the circle as the normal, the reflected wave of the sound ray incident on the area indicated by the symbol A2 is
Transceiver 2 on the receiving side without returning to ultrasonic transducer 3
The direction of propagation of the ultrasonic wave toward b (to the right) is opposite (to the left), and only the ultrasonic wave in the area indicated by the symbol A1 is directed to the transducer 2b on the receiving side. This improves the apparent propagation directivity of the transmission,
The multiple reflection of the ultrasonic transducer inside the transmitter / receiver is reduced, and as a result, the generation of wraparound waves in the pipe is reduced and the S / N of the received wave is improved.

FIG. 3 is a block diagram showing another embodiment of the present invention. FIG. 3A is a side sectional view and FIG. 3B is a top view thereof. Note that the reference numerals assigned to the respective units are the same as those in FIG.
That is, this embodiment is characterized in that the tip of the wedge is tapered, as is apparent from FIG.
The space between the tapered portion and the case 5 is filled with a rubber-like filler (also referred to as a sound absorbing material) 7 as in the case of FIG. Absorbs part of the sound. The reason why the tip of the wedge is tapered will be described below with reference to FIG.

FIG. 4 shows an example in which the taper at the tip of the wedge is set to 120 degrees. In this figure, sound rays u and t emitted from the ultrasonic transducer 3 in the transducer are on the wall 4 in the transducer.
C, the direction of propagation of the ultrasonic wave toward the transmitter / receiver 2b on the receiving side is opposite to the propagation direction of the ultrasonic wave, and the angle of the sound ray in the top view of FIG. If so, all the sound rays are in the opposite direction to the propagation direction of the ultrasonic wave toward the transducer 2b on the receiving side. If the angle of the sound ray in the top view of FIG.
Only the sound ray in the area indicated by 1, A3 is the transducer 2b on the receiving side.
, The apparent propagation directivity of the transmission is improved, and the generation of the wraparound wave in the pipe is reduced, and the S of the received wave is reduced.
/ N is improved.

FIG. 5 shows an example in which the taper at the tip of the wedge is set to 90 degrees and the center position of the taper is shifted. In this case, the angle of the sound ray in the top view of FIG.
Within this range, only the sound rays in the areas indicated by the reference signs A1 and A3 are directed to the transmitter / receiver 2b on the receiving side, and the directivity of the ultrasonic waves emitted from the ultrasonic transducer 3 is not good. However, good transmission and reception are possible. The other points are the same as those in FIG. 2 or FIG.

In the case where the tip of the wedge is tapered, it is possible to more reliably avoid the reflected sound ray from entering the ultrasonic vibrator by considering the distance between the ultrasonic vibrator and the tapered portion. . FIG. 6 illustrates this, and L indicates the distance between the ultrasonic transducer 3 and the tapered tip (the reflecting wall 4C of the transducer). That is, if θ in the figure is set to the side lobe generation angle, most of the sound ray emission angles of the ultrasonic vibrator 3 are equal to or smaller than the side lobe generation angle, and thus the ultrasonic vibrator in the transducer is used. Can be greatly reduced. Note that there is a relationship as shown in the following equation between the distance L and θ. L = d · [Tan θr + Tan (2θr−θ)] / [1−Tan θ · Tan (2θr−θ)] (1) where θr is the set angle of the reflecting wall 4C, and d is the outer diameter of the ultrasonic transducer. Indicates the dimensions, and 2θr> θ.

The side lobe occurrence angle θ differs depending on the outer diameter d of the ultrasonic transducer, and has a relationship as shown in FIG. A symbol B in the figure indicates directivity and is represented by a Bessel function of the first kind. Z is calculated from the equation shown in the figure using θ, the outer diameter d of the ultrasonic transducer, the wavelength λ of the ultrasonic wave in the wedge, and the like. Further, the directivity B has a characteristic as shown in FIG. 8, for example. The symbol Sdp in the figure indicates a side lobe. That is, the ultrasonic transducer 3 shown in the equation (1)
The distance L between the tapered tip and the taper tip is obtained by calculating the side lobe generation angle θ from the outer diameter dimension d of the ultrasonic transducer 3 with reference to FIG. 8, and calculating the equation (1) from this angle θ. Obtainable.

[0017]

According to the present invention, the cross section of the wedge to which the ultrasonic vibrator is attached in the longitudinal direction of the pipe is formed as a divided circle or a divided ellipse, or a taper is formed at the tip of the wedge. Therefore, the apparent propagation directivity of the received wave is improved, and the generation of the wraparound wave of the pipe is reduced, and the multiple reflection in the transmitter / receiver is reduced, so that the trailing of the wraparound wave of the pipe is reduced, and the As a result, S of the received wave
/ N is improved and the measurement accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining an operation of FIG. 1;

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining the operation when the taper of the wedge tip is set to 120 degrees in FIG. 3;

FIG. 5 is an explanatory diagram for explaining the operation when the taper of the wedge tip is set to 90 degrees and the center position of the taper is shifted in FIG. 3;

FIG. 6 is an explanatory diagram for explaining a distance between an ultrasonic transducer and a tapered portion.

FIG. 7 is an explanatory diagram for explaining directivity of an ultrasonic transducer.

FIG. 8 is an explanatory diagram for explaining a relationship between a generation angle of a side lobe and an outer diameter of an ultrasonic transducer.

FIG. 9 is a schematic diagram showing a conventional example of an ultrasonic flowmeter.

FIG. 10 is a schematic diagram showing another conventional example of an ultrasonic flowmeter.

FIG. 11 is a configuration diagram illustrating an example of a conventional transducer.

FIG. 12 is a perspective view for explaining a loop wave in a pipe.

FIG. 13 is an explanatory diagram for explaining a direct reception wave and a loop wave in a pipe.

FIG. 14 is a waveform diagram for explaining the relationship between a direct reception wave and a loop wave.

FIG. 15 is an explanatory diagram for explaining a propagation mode of an ultrasonic wave emitted from an ultrasonic transducer in a conventional transducer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piping, 2a, 2b ... Ultrasonic transducer, 3 ... Ultrasonic transducer, 4 ... Wedge, 4A ... Wedge bending part, 4B ... Ultrasonic transducer mounting surface, 5 ... Case, 6 ... Cable, 7 ... Sound absorbing material (rubber filling), 10 ... Acoustic coupling material, 15 ...
Pipe inner wall surface, 16: Pipe outer wall surface, 20: Fluid.

Claims (2)

(57) [Claims] 1. A pair of transducers comprising an ultrasonic transducer and a wedge to which the ultrasonic transducer is adhered and capable of transmitting and receiving ultrasonic waves, are arranged opposite to each other on the outer wall surface of the pipe so as to face each other,
The difference between the propagation time of the sound wave from the ultrasonic transducer on the upstream side to the ultrasonic transducer on the downstream side and the propagation time of the sound wave from the ultrasonic transducer on the downstream side to the ultrasonic transducer on the upstream side In a transmission ultrasonic flowmeter for measuring a flow velocity or a flow rate, a cross-sectional shape of a wedge in at least one of the pair of transducers in a longitudinal axis direction of a wedge is a fraction circle or a division ellipse. A transmission type ultrasonic flowmeter characterized by the above. 2. A pair of transducers comprising an ultrasonic vibrator and a wedge to which the ultrasonic vibrator is bonded and capable of transmitting and receiving ultrasonic waves are arranged opposite to each other on the outer wall surface of the pipe so as to be shifted from each other,
The difference between the propagation time of the sound wave from the ultrasonic transducer on the upstream side to the ultrasonic transducer on the downstream side and the propagation time of the sound wave from the ultrasonic transducer on the downstream side to the ultrasonic transducer on the upstream side A transmission ultrasonic flowmeter for measuring a flow velocity or a flow rate, wherein a tip of a wedge in at least one of the pair of transducers is tapered.